Today there is a massive quantity of nuclear waste accumulating across the world. In the US alone there are more than 70,000 metric tons (MT) of high-level solid waste (HLW) being stored in cooling pools and in concrete casks on the surface. This surface operation is very costly typically costing hundreds of millions of dollars annually. The HLW is generally called spent nuclear fuel (SNF) and consists of thousands of nuclear fuel assemblies which have been removed from operating nuclear power plants. These fuel assemblies are highly radioactive and also thermally active and continue to generate sensible heat which must be safely removed by maintaining these assemblies in cooling tanks at the onsite surface storage site. There are approximately 80,000 individual fuel assemblies being stored today in the US and about 15,000 MT being added annually. There is a significant need for new mechanisms and processes to safely get rid of the surface storage of this radioactive waste and to sequester this SNF waste in a safe manner. In this application HLW and SNF are used interchangeably to describe the solid nuclear waste product.
In this application the word capsule and canister may be used interchangeably with the same meaning; and HLW and SNF describing nuclear waste may also be used interchangeably herein.
Current scientific knowledge teaches that the conversion of nuclear waste to an acceptable waste form requires either, (a) that the wastes be separated from the other constituents and processed separately, or (b) that the wastes together with the other constituents be processed together. Both processes present a variety of technical challenges. Due to the radioactivity and toxicity of the wastes, separation can be both hazardous, expensive and prone to human-induced accidental problems.
To date, and based on the prior art, in order to provide a satisfactory and economical final disposal of these wastes, it is desirable that the wastes be processed into a final form without the hazardous and expensive step of removing the other constituents. It has been understood that the waste in this final form prevents removal of the fissile constituents of the wastes and further immobilizes the waste to prevent degradation and transport of the waste by environmental mechanisms.
Several methods for providing an acceptable final form for waste are known in the art, including:
(a) Vitrification to produce borosilicate glasses having waste constituents bound within the glasses has been shown as an effective method for treatment of low volumes of HLW. In the vitrification process, wastes are mixed with glass-forming additives and converted into an amorphous glassy form by high temperature melting and cooling. There are several inherent technical drawbacks of vitrification. A further drawback of vitrification arises due to the low solubility of many of the waste components of interest in glass which prohibits large concentrations of the waste components in the final glass form. This low solubility greatly increases the required volume of the final waste form for a given volume of radioactive waste components of interest, thus unfortunately the waste volume “grows.” This makes the overall nuclear waste product even larger than the original thus requiring more storage and costs.
(b) Ceramification produces another form of nuclear waste. It can be accomplished by the incorporation of waste components of interest into a synthetic rock (synroc) which is a ceramic material. The synroc process has been fully developed and as commercialized in Australia (ANSTO) produces a crystalline final waste form and involves several complex expensive steps involving high temperatures and pressures utilized to successfully create a suitable final waste form.
The cost associated with these two primary methodologies is prohibitive. Published information from the US Hanford Nuclear facility which is designed for vitrification operations has a projected cost level of $16 Billion.
Published information from the ANSTO facility which is designed for ceramification operations has a projected cost of hundreds of millions of dollars. Commercial revenues are expected to pay for development. Both processes listed herein (e.g., vitrification and/or ceramification) increases a volume of waste product to be stored. Thus, use of these processes may be counter-intuitive with a goal of minimizing an amount of nuclear waste. That is, use of these processes creates even more nuclear waste that needs to be safely handled and stored.
Based on the inherent shortcomings of the prior art, there exists a critical need for an effective, economical method for developing and utilizing an acceptable nuclear waste process for nuclear waste products; a process that precludes the need for all the expensive, time-consuming and dangerous intermediate operations that are currently being used or contemplated to render the nuclear waste in a form that eventually, still has to be buried in deep underground repositories. An approach is needed that minimizes these intermediate steps. To solve the above-described problems, the present invention provides a system and method to dispose of the nuclear waste currently accumulating on the surface.
The novel approach as taught in the application provides a methodology wherein the waste disposal operations go directly from the existing fuel assembly rod cooling ponds to the underground disposal repository with minimal additional effort and without the afore-listed intermediary steps of vitrification and ceramification.
It is to these ends that the present invention has been developed.